土石混合体的剪切面分形特征及强度产生机制

Fractal characteristics of shear failure surface and mechanism of strength generation of soil-rock aggregate

基于考虑含石量、含水率、块石岩性、初始孔隙比、法向压力5个影响因素的土石混合体室内大型直剪试验,利用剪切面在分形几何学上的统计规律和颗粒流数值模拟方法得到的直剪试验中颗粒的相互作用规律,对土石混合体的抗剪强度产生机制进行研究。结果表明:(1)土石混合体的剪切面呈不规则的起伏形态与块石的存在关系密切,且具有较好的分形特征,分形维数随着含石量和块石强度的增大、含水率和法向压力的减小均呈增大趋势;(2)含石量高于40%时,黏聚力小于30 k Pa;(3)内摩擦角随着含石量的增大、块石强度的增大、含水率的降低、初始孔隙比的降低、法向压力的降低均呈增大规律,且与分形维数满足正相关函数关系;(4)块石附近应力集中较明显,剪切过程中,颗粒间的接触力主要通过迎着剪切方向的接触面传递,而背着剪切方向的颗粒接触面基本不传递力;(5)内摩擦角φ等于剪切面上与颗粒本身接触性质有关的接触面内摩擦角θ0和与剪切面分形维数有关的接触面倾角θi之和,利用此机制可解释直剪试验中强度参数的变化规律。

The large-scale direct shear test was conducted to soil-rock aggregate with different rock contents,water contents,rock lithology,initial void ratios and normal pressures. The shear strength mechanism of soil-rock aggregate was analyzed through the statistical analysis of fractal geometry of shear surface and the numerical simulation of particle interactions in the direct shear test with the particle flow code. The results indicate that the irregular topography of the shear failure surfaces of soil-rock aggregate are closely related to the existence of rock blocks and presents the fractal characteristics. The fractal dimension increases gradually with the decreasing of water content and normal pressure and the increasing of rock content and strength. If the rock content is more than 40%,the cohesion will be less than 30 k Pa. The internal friction angle increases with the increasing of rock content and strength,the decreasing of water content,initial void ratio and normal pressure,and it has a positive correlation with the fractal dimension. The stress concentration happens near the rock particles. In the process of shearing,the contact force between the particles transfer mainly through the surface in the direction of shearing,but the contact surfaces back to the shear direction does not appear to transfer force. The internal friction angle j is equal to the sum of θ0 and θi,where θ0 is the internal friction angle of the contact surface of particles on the shear plane related to the particle＇s properties and θi is the dip angle of the contact surfaces of particles related to the fractal dimension on the shear surface. The variation of shear strength parameters in the shear test can be explained with this mechanism.